Matching pixel density ratios across multiple objects
You can easily achieve this with wonderful add-on TexTools. I'm using current version 1.2.0.

How to install add-on?

Here is a screenshot from add-on site with whole explanation (I'm posting this one just to keep it safe):



Steps:




Make a Material with texture (important!) or use Checker Map from add-on.
In UV Editor (where TexTools lives) set your texture size.
With one object selected use Texel Density picker.
Select all objects and apply Texel Density.